Technical Field
The present invention relates in general to solid oral compositions, which provide an acidic reaction when dissolved in an aqueous liquid like saliva. More particularly, the present invention relates to acidic solid oral compositions with reduced erosive potential in saliva and to the use of a calcium component and an acid component in particular amounts for reduction of the erosive potential. The invention also relates to a method for stimulating saliva production, and to the use of a calcium component and an acid component for the manufacture of an acidic solid oral composition for alleviating the sufferings of an individual having impaired saliva production. Furthermore the invention relates to a method for determining the erosive potential of an oral composition in saliva.
Description of the Related Art
Dental erosion is the loss of dental hard tissue by a chemical process that does not involve bacteria and is therefore not associated with dental plaque. One of the most important factors with respect to dental erosion is extrinsic exposure to acid. Dental erosion has been shown to be an increasing threat to dental health, and frequent soft drink consumption as well as consumption of acid-containing foodstuffs (citrus fruits and sweets) are important factors in the development of dental erosion. The general awareness of dental erosion is increasing rapidly. It is therefore important for manufacturers to think of new ways to develop foodstuffs that satisfy consumers' need of acidic stimuli and that at the same time do not cause or reduces dental erosion.
Generally, low pH in the oral cavity and around the teeth is the major cause of dental erosion. The hard part of human teeth is composed of hydroxyapatite crystals (HAp) (Ca10(PO4)6(OH)2). In the teeth the HAp crystals are arranged in a condensed structure making up the hardest tissue in the body. However, if the teeth are exposed to fluids with a low pH (like acidic soft drinks or saliva containing dissolved acidic candy) the HAp crystals will dissolve and dental erosion will develop due to shortness of Ca2+, PO43− and OH− ions in the fluid (components of HAp).
Beverages supplemented with significant levels of calcium for nutritional purposes have been suggested in the prior art. Dietary calcium inadequacy may be a contributing cause to osteoporosis, at least within some populations. For example, a positive correlation between calcium intake and bone mass has been found across many age groups. It has also been suggested that the level of calcium intake earlier in life directly influences the peak bone mass achieved at skeletal maturity.
U.S. Pat. No. 5,028,446 discloses a process for preparing rapidly solubilized calcium fumarate for use in the production of calcium fortified beverages. The process involves the preparation of a mixture of fumaric acid and a calcium-containing base, wherein the mole ratio of the calcium to the fumarate is ranging from 1:2 to about 1:1. The mixture of fumaric acid and calcium is indicated to possess an improved solubility characteristic usable in the production of calcium fortified beverages, such as tea.
Another calcium-fortified beverage is disclosed in EP 227 174. The beverage is substantially free of sugar alcohol and comprises a certain weight ratio of calcium to a mixture of citric, malic, and phosphoric acid of ¼ to 1/7. The beverage is said to have a satisfactory initial taste and mouth feel, substantial freedom from objectionable aftertaste and desirable calcium absorbability/bioavailability properties. Typically, the pH of the produced beverages is around 4.3.
A dry mixture intended for reconstitution comprising citric acid and one or more calcium compounds is disclosed in WO 88/03762. The instant beverage may comprise a mole ratio of calcium/citric acid between 0.6 and about 3.0. The solubility of the mixtures having varying ratios between calcium and citric acid depended on the pH. The solubility was tested for pH values between 2.0 and 7.0, an actual drink as prepared having a pH of 4.15 and above. The composition has a utility as a liquid dietary calcium supplement.
U.S. Pat. No. 3,734,742 discloses a sealed or canned bottled aqueous beverage containing at least about 80% of water and having a pH of from 2.0 to 3.4, an ascorbic acid content of from 0.056 to 1.120 mg/ml and a ferrous ion content of from 0.008 to 0.15 mg/ml. The object of this US patent is to obtain a beverage supplemented with iron and ascorbic acid.
None of the above mentioned references relate to dental erosion.
As mentioned in the introduction, acidic compositions for consumption tend to erode tooth components, notably the content of hydroxyapatite. Several publications address this issue. EP 634 110 A2 pertains to a nutrient, vitamin and mineral fortified, fruit based liquid foodstuff having an acid content of at least 5 g/l as tartaric acid and a content of calcium phosphate of at least 2 g/l. The pH is below 4.5, with actual values between 3.9 and 4.15. The calcium phosphate is said to reduce the negative influence of the acidic liquid foodstuff on the tooth substance. Another liquid oral composition comprising a calcium compound and an acid compound is disclosed in WO 97/30601. The liquid composition contains calcium in the range of 0.3 to 0.8 moles per mole of acid and as an important feature the amount of calcium and acid in the composition is selected so that the pH of the composition is from 3.5 to 4.5. A further acidic beverage, which is said to inhibit the erosion of tooth enamel, is disclosed in U.S. Pat. No. 5,108,761. The beverage according to U.S. Pat. No. 5,108,761 includes calcium citrate malate for reduction of dental erosion.
An acidic medical preparation has been disclosed in U.S. Pat. No. 4,080,440 disclosing a process for remineralising dental enamel. The process implies applying a freshly prepared metastable aqueous solution to the tooth surface. The solution has a pH of about 2.5 to about 4.0 and comprises a soluble calcium salt and a soluble phosphate salt in such amounts that the molar ratio of calcium ions to phosphate ions is in the very broad range from 0.01 to 100. The preparation is not intended for being consumed.
Also edible or chewable solid or semi-solid compositions, which show a reduced tendency to erosion of teeth have been disclosed in the prior art. WO 98/13013 discloses e.g. a chewing gum or a candy capable of remineralising tooth lesions. The composition in question comprises a cationic component comprising at least one partially water-soluble calcium salt, an anionic component comprising at least one water-soluble phosphate salt and a separating component. The pH of the composition when dissolved in water or saliva is from greater than about 4.0 to about 10.0. Because of the partial water-solubility of the calcium salt, the calcium cations and the phosphate anions in the mixed aqueous composition remains soluble for a period of time sufficient to allow the cations and anions to diffuse through the surface of the tooth to the subsurface or dentine, where the diffused cations and anions react to form an insoluble precipitate on the lesion for remineralisation thereof.
WO 99/08550, having the same inventor as WO 97/30601, discloses an acid containing solid or semi-solid composition with reduced tooth erosion. The composition contains calcium in the range of 0.3 to 0.8 moles per mole of acid and the proportion of calcium and acid in the composition is selected so that the effective pH of the composition, when dissolved in a liquid such as water, is from 3.5 to 4.5. While a tooth protection may be obtained by using this composition, the saliva stimulating effect will be limited due to the comparatively high 5 pH value, and the taste experience thereby impaired. This is particularly critical in relation to such products as boiled sweets, candies, lollipops, jellies, chewing gums, drops, pastilles, lozenges, tablets, ice cream and sorbets.
In US 2004/0091517 A1 having the inventor of WO97/30601 and WO99/08550 as co-inventor, acidic oral compositions having effective pH values down to 2.2, especially acid beverages with a pH between 2.2 and 5.5, are disclosed. The invention according to said application resides in the use of a polyphosphate being a phosphate polymer wherein the number of phosphate groups (n) is at least 3, as a tooth erosion inhibitor. The polyphosphate may be used in conjunction with calcium being present in amounts up to 0.8 moles per mole of acidulant. However polyphosphates are undesirable from different points of view, particularly in the preparation of hard-boiled candy and other products, which are subjected to heating. By heating of the acidic composition there is a risk of the polyphosphate becoming converted to other phosphates, which are known to have an unpleasant taste. Furthermore, by having both calcium and phosphate in high concentrations, there is a risk of the calcium precipitating out as non-useful calcium phosphate compounds.
The present inventors suggest decreasing the pH in order to obtain a better taste experience and a pronounced saliva stimulating effect. This has been possible while maintaining a composition, which is non-erosive in saliva—without the use of a polyphosphate as disclosed in US 2004/0091517 A1.
The increased saliva production results in an increased protective effect from the constituents of the saliva itself. As a further interesting point, the non-erosive effect of the composition seems to be obtainable even in so-called “dry-mouth” individuals suffering from impaired saliva secretion.
This surprising finding is the result of extensive research carried out by the present inventors, which among others has resulted in a new test method for erosive potential, which in a simple and reliable manner takes into account the complex conditions in saliva in the human mouth in the presence of the acidic oral composition, such as a candy. This test method represents a particular aspect of the present invention.
When solid and semisolid compositions are sucked, saliva becomes the matrix for the compositions, and thereby saliva influences all effects that the compositions may have on teeth. The method according to the invention provides, in contrast to theoretical calculations based on physical chemistry, the unique feature of accounting for all protective factors present in human saliva, organic as well as inorganic. These factors include the salivary proteins (around 2 mg/ml), the saliva buffer capacity, the saliva calcium and phosphate, saliva fluoride, and trace amounts of other ions present in saliva. The salivary proteins have the ability to form a protective coating, also known as the acquired pellicle, on the surface of teeth. Due to this ability, the salivary proteins will protect teeth and tooth substance against acid induced erosion. However, the effect of this protein coating on tooth erosion in different individuals cannot be quantified by any known methods of calculation, it has to be subjected to testing. The saliva buffer capacity, which originates from salivary bicarbonate, phosphate, and proteins, will also protect teeth and tooth substance against acid induced erosion, and this effect also has to be accounted for by the test method. Thus, when an acidic oral composition is dissolved in saliva, the pH will drop, however, the pH drop will be counteracted by the three salivary buffer systems resulting in an increased salivary pH and thereby reduced erosive effect. Saliva also contains some calcium and phosphate, which will help to increase the degree of saturation with respect to hydroxyapatite and thereby decrease acid induced erosive effects. In this context, saliva also contains fluoride, mainly originating from foodstuffs and toothpaste, and this fluoride will increase the effective degree of saturation with respect to tooth substance, and thereby also decrease acid induced erosive effects. Finally, trace amounts of other ions originating from foodstuffs and drinking water may also have an effect on tooth substance dissolution. In concert, the three last factors may have considerable protective effects that cannot be directly predicted by calculation and therefore also needs to be tested by the method provided. The method according to the invention provides an efficient means for determining the demineralization of hydroxyapatite and thereby evaluation the erosive potential of any solid and semisolid composition dissolved in saliva.